Rotating turbo machinery, such as fan blades, turbine and compressor components, experience high vibration and tensile stresses during operation. These stresses make the components susceptible to high cycle fatigue (HCF) and stress corrosion cracking (SCC) failure mechanisms, which limit the service life of the components. Prolonged exposure to extreme operating conditions can also lead to the development of fatigue cracks in areas of the component subject to high operational stresses. HCF life is also reduced by the occurrence of foreign object damage (FOD). FOD locations act as stress concentrators that speed up the initiation and propagation of fatigue cracks. FOD, especially along the blade leading and trailing edges, significantly reduces the service life of aerospace components.
HCF, SCC, and FOD necessitate periodic inspection and repair or replacements of limited life parts (LLP) in an engine if any cracks or specific FOD depth is found. The periodic inspection of parts increases maintenance cost, and the replacements of the parts usually affects the flight readiness and operating costs of the engine. Integrally bladed rotors (IBRs) are one of the most expensive component in an engine because of the limited life and required inspection and maintenance due to stress related failure mechanisms and FOD. If a blade on an IBR is damaged, the whole IBR will be removed from the engine to be repaired or replaced. The repair and/or replacement of such a complex component is expensive and takes a significant amount of time. IBRs can be made with a five axis milling machine tool that is controlled digitally with computer numerical controls (CNCs).
Surface enhancements of blades (including IBRs) increase their fatigue strength, FOD tolerance, resistance to stress related failure mechanisms and save in maintenance costs. This enhancement can be achieved through a peening process, which induces compressive residual stress to the surface of the blade. The magnitude and depth of the residual stress depend on the method used to peen the surface.
Laser shock peening (“LSP”) is one of several peening processes that can be used to enhance surface properties of parts. LSP is often used to enhance surface properties and increase the resistance of aircraft gas turbine engine compressor components and fan blades to FOD, improving high cycle fatigue life. LSP can create about 1 to 2 mm depth of residual compressive stresses into part surfaces to inhibit the initiation and propagation of fatigue cracks.